| The Guizhou region has abundant coal measure shale gas resources,with great exploration potential.This article takes the Dahebian syncline coal measure shale in western Guizhou as the research object.Through experiments such as analysis of shale mineral composition,determination of organic carbon content,identification of microscopic components,and measurement of vitrinite reflectance,the organic geochemical characteristics,mineralogical characteristics,and lithofacies distribution of coal-bearing shale are explored;The organic matter separation experiment was used to extract kerogen samples from coal-based shale,combined with scanning electron microscopy observation,gas adsorption and small-angle scattering experiments,to explore the pore development characteristics and main controlling factors of coal-based shale at different scales,different types and different connectivity.The results showed that the organic matter abundance of coal shale in the study area was high,and the TOC content was between 1.2%～13.4%,with an average of 6.4%.The kerogen type is type III.and the vitrinite reflectivity R_ois between0.68%～0.95%,with an average of 0.83%,which is in the mature stage.The mineral composition of coal-based shale in the study area was mainly clay minerals,quartz is second.Among them,the clay minerals were mainly kaolinite,followed by chlorite,and the content of Eamonn mixed layer was less.According to the mineral composition,the brittle mineral index of the samples was calculated at an average of 52.2%,indicating that the coal-based shale reservoirs in the study area had good fracturability.According to the mineral composition and TOC content of shale,the coal shale samples were divided into six lithofacies:high organic siliceous mixed shale facies,high organic siliceous shale facies,low organic clay shale facies,high organic clay shale facies,medium organic clay shale facies and low organic siliceous shale facies.Pore types mainly include inorganic pores,organic pores,and microcracks.Among them,the inorganic pores are mainly inkbottle type,and the organic pores are round.The pores in shale whole rock samples were mainly microporous and mesoporous,while the micropores,mesopores and macropores in kerogen samples were well developed.Micropores and mesopores in the whole rock have the greatest influence on fractal dimension,which is the main reason for the heterogeneity and complexity of pore structure.The scattering intensity of kerogen samples was significantly higher than that of whole rock samples,reflecting the development of more micropores and mesopores in kerogen.The connected pores accounted for 11%～88%and the average was 49%,and the closed pores accounted for 12%～89%,with an average of 51%.The connected pores in the kerogen sample accounted for 3%～47%,with an average of 17%,and the closed pores accounted for 53%～97%,with an average of 83%.Clay mineral content and TOC content were the main factors affecting the development of connected pores,clay minerals mainly affected the development of connected pores,which were basically not related to the development of micropores and macropores,while TOC content had an impact on the development of connected pores,mesopores and macropores.The proportion of closed pore volume was negatively correlated with TOC content,and positively correlated with maturity R_o.The pore development of the whole rock was mainly affected by the mineral content of quartz and clay,the quartz content mainly affected the development of micropores and mesopores in closed pores,and clay minerals had an impact on the development of micropores,mesopores and macropores.The results of connected through pores,closed pores and overall pore volume distribution of different rocks showed that clayaceous shale was the most favorable type of shale lithofacies,and the development of inorganic pores of siliceous minerals was greatly affected by TOC content.Mixed shale is affected by carbonate minerals and has poor overall pore development. |
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